The present embodiments relate to Doppler ultrasound, such as color flow (e.g., flow mode) imaging or Doppler mode (e.g., spectral) imaging. By transmitting a plurality of pulses (e.g., pulsed wave (PW)) or a continuous wave (CW) at one more locations, a Doppler response is generated in response to received echo signals. For spectral Doppler, the frequency spectrum of the object's motion or flow for a single spatial region is estimated and displayed as a function of time. Spectral Doppler ultrasound imaging provides an image of spectra as velocity values (vertical axis) modulated by energy as a function of time (horizontal axis) for a gate location. The spectra may be used for studying fluid flow or tissue motion within a patient.
Spectral Doppler in medical ultrasound is limited in sensitivity due to electronic and acoustic noise and signal processing dynamic range. On difficult to scan patients, the signal-to-noise ratio is often insufficient to visualize the signal of interest, such as the maximum velocity of a cardiac jet or the presence of flow in a deep artery or vein. In other situations, the speckle noise degrades the image quality in the Doppler strip.
Other than using better quality electronic components and transducers, the noise may be reduced using image processing. For example, speckle noise is located in a Doppler strip and reduced. As another example, edges between noise and actual signal are found in the Doppler strip and enhanced. These processes use post-processing non-linear filters, but may not sufficiently increase the signal-to-noise ratio and/or reduce speckle.